Synchronizing system



Aug. 11, 1936. E. R. MQRTON SYNCHRONIZING SYSTEM Original Filed Dec. 28,1927 ORNE Y /NVEN7'O/-? BfDMl/ND fi. MORTON H smwwa Patented Aug. 11,1936 UNITED STATES PATENT OFFICE SYNCI-IRONIZIN G SYSTEM:

Application December 28, 1927, Serial No. 242,998 Renewed February 17,1931 20 Claims.

This invention relates to synchronizing systems and particularly to amethod and means for maintaining apparatus employed at differentstations of television and picture transmission systems in synchronism.

It has heretofore been proposed in connection with picture transmissionsystems to transmit unmodulated carrier current of increased amplitudeduring the underlap period of the picture to maintain the receivingpicture drum in synchronism with the picture drum at the transmittingstation. The picture drums are driven by La Cour motors, each of whichis actuated by a mechanical resonance means in the form of a tuningfork, for maintaining each motor at a substantially constant speed. Whenthere is a departure from synchronism the synchronizing carrier currentis employed to vary the position of weights on the tines of the tuningfork at the receiving station for increasing or decreasing the speed ofthe motor at this station.

This invention contemplates a synchronizing system in which the speed ofone of the elements to be maintained in synchronism is controlled byapparatus comprising electrical resonance means having a steepfrequency-response characteristic, and means under the control of asynchronizing control station are provided for varying the naturalperiod of the resonance means when these elements move out of phase.

In another aspect of the invention there is provided a rotating elementcontaining unevenly spaced light transmitting portions for scanning afield or a portion of a field along groups of parallel linessuccessively, and means associated with the rotating element is employedfor producing a synchronizing impulse between groups of parallelscanning lines.

There is disclosed in Patent No. 1,663,891, granted to H. M. Stoller andE. R. Morton, March 2'7, 1928, a speed regulating system which may beemployed in connection with this invention. In this system a highfrequency generator ismechanically connected to a motor for supplyingalternating cu'rrent through a tuned circuit to the grid of a vacuumtube. The speed of the motor is controlled, in response to variations inthe frequency of the generator, through a field winding of the motorconnected in the space current circuit of a second vacuum tube coupledto the first.

In the specific embodiment of this invention, herein shown and describedfor the purpose of illustration, a regulating system, similar to thatdisclosed in the copending application referred to above, is employed ina television system, such as disclosed in a copending application of F.Gray, Serial No. 227,649, filed October 21, 1927, for controlling thespeed of the motors which turn the. scanning apparatus at thetransmitting station 5 and the image reproducing apparatus at thereceiving station. For the purpose of scanning the object, an image ofwhich is to be viewed at the receiving station, a motor at thetransmitting station turns a disc having a plurality of spirallyarranged apertures therein through which light is directed uponsuccessive elemental areas of the object. One or more photoelectriccells are provided for receiving light reflected from the object and forgenerating a current which varies in accordance with the light intensityvariations.

A hole in a scanning disc displaced in a radial direction from thespirally arranged holes and positioned on a radius extending between thefirst and last holes of the spiral is provided for synchronizingpurposes. Light passing through this hole is directed upon one of thephotoelectric cells preferably through a system of mirrors, for settingup a synchronizing electrical impulse once per revolution of thescanning disc. These synchrcnlzing impulses are transmitted over thesame line that is employed for transmitting the image currents to thereceiving station where they areimpressed upon a circuit which controlsthe capacity of a condenser associated with the tuned circuit of a motorspeed regulating circuit such as referred to above, thereby maintainingthe apparatus at the two stations in phase.

The following is a detailed description of the embodiment of theinvention referred to above. Reference is made to the accompanyingdrawing in which,

Fig. 1 shows a television system employing apparatus which issynchronized in accordance with the present invention and Fig. 2 is anenlarged view of a portion of the apparatus employed at the transmittingstation for scanning and synchronizing purposes.

Referring now to the drawing, the television system shown is adapted togenerate electrical currents corresponding to the light reflectingproperties of elemental areas of an object 50 at the transmittingstation, transmit these currents over a transmission channel such as theline 5| and, by means of apparatus at the receiving station, to form animage of the object 50 on the eye of an observer 52. The object islocated in front of a scanning apparatus which comprises an arc lamp 53and an optical system for causing a slender pencil of substantiallyparallel rays of intense light to sweep across the field in front of thescanning apparatus and scan the object in a series of successiveparallel lines. The optical system includes a scanning disc 58 which hasa number of small circular apertures (shown in Fig. 2) arranged in aspiral extending aroundthe disc near its rim. Light from the are 53 isdirected by a lens system 54 so that an intense beam of light passesthrough each aperture as it moves across the illuminated area of thedisc. An opaque screen 58 in front of the disc is provided with arectangular opening 51 of such width as to admit light from only oneaperture at a time. Lens 59 bends the slender pencil of parallel rayspassing through the aperture and the opening 51 to form an image of themoving aperture on the object 50. As a result of this arrangement theobject is completely scanned once for each revolution of the disc in aseries of successive parallel lines by a small, rapidly moving,intensely bright spot of light. As the spot of light passes over theobject, light is diffusely reflected therefrom and a portion of thereflected light falls on the photosensitive surface of a large aperturephotoelectric cell 60 which generates an electric Wave varying inaccordance with the light intensity variations reflected from theobject. This type of scanning apparatus is described in more detail inthe application of Gray referred to above.

The image waves generated by the photoelectric cell are amplified by anelectric discharge amplifier 6| and transmitted through a. transformer83 to the line 5| which connects the transmitting and receivingstations.

At the receiving station the image waves from the line 5| aretransmitted through a transformer 84 to an electric discharge amplifier62 by which they are amplified and impressed upon a neon glow dischargelamp 63 arranged in front of a scanning disc 64 similar in constructionto the scanning disc located at the transmitting station. In front ofthe disc there is located an opaque screen 82 having an opening 85 ofsuch size that at any one time only one of the apertures of the disc 64is in the field of view of the observer 52. The lamp 63 is preferably ofthe type disclosed in detail in Patent No. 1,865,516, granted to F.Gray, July 5, 1932. The optical field defined by the opening 85 andilluminated by light coming from the lamp 53 through the. movingapertures of the disc 64 is viewed by the observer 52 without the aid ofany optical system. The observer sees at any instant a single aperturein the same relative position as a spot of light on the object 50 at thetransmitting station and the brightness of the aperture corresponds tothe amount of light reflected from that particular elemental area of theobject. On account of persistency of vision the observer c0nsequentlysees an apparent image of the object on the front surface of the disc64, complete views of the object being transmitted at the rate of about18 per second so that the object can be seen in motion.

The disc 56 at the transmitting station is driven by a motor 86 which ismaintained at a substantially constant speed by speed regulatingapparatus 81. This motor and speed regulating apparatus may be the sameas that employed at the receiving station for driving the disc 64 at asubstantially constant speed and which will -now be described.

The disc 64 is driven by the motor 3 having a commutator 4 and a shuntfield winding 5 operation of the motor.

supplied with direct current from a source 6.

The motor is also provided with slip rings "i and 8 connected tocommutator bars apart. These slip rings are provided with brushes con;nected to a transformer 9 for supplying alternating current to theregulator circuit during the The motor is also provided with a regulatorfield winding it! which is so wound as to supply flux which aids thatsupplied by the winding 5. Directly connected to I the motor 4 (ormounted in the same frame) is a high frequency inductor generator ii,comprising a toothed rotor 52 and a field structure 3 on which ismounted a field coil Hi connected to the direct current source 6 and agenerator I coil 5. As the teeth of the rotor pass the pole pieces ofthe field structure, the reluctance of the magnetic circuit is varied,thereby generating electrical variations of high frequency in thewinding l5.

The regulator circuit proper comprises a detector tube l5, having acathode H, a grid l8 and a plate i9, and an amplifier tube 20, having acathode 2|, a grid 22 and a plate 23. Heating current is supplied to thecathodes l7 and 2| rei spectively from the secondary windings 24 and 25of the transformer 9. Space current is supplied to the tubes "1 and 20,respectively, from the secondary windings 26 and 21, each of which isshunted by a condenser. The direct current source source 8 is employedfor negatively biasing the grids of both tubes as explained below. Atuned circuit 33 comprising a fixed condenser 29, a variable condenser35 and an inductance 30 is connected to the winding l5 of the generator3 I. The inductance coil 30 is connected in the grid circuit of thedetector tube I6 in series with the source 6. The circuit may be tracedfrom the grid l8, inductance coil 30, negative terminal of r source 6,positive terminal of source 6, conductor 34 to cathode H. A resistance3| shunted by condenser 32 is connected in the plate circuit of the tubel6. Condenser 32 is given such a value that the voltage across theterminals of the resistance 3| is proportional to the value of the 4high frequency potential impressed on the grid 8 and practicallyindependent of the low frequency plate current source. Resistance 3| isconnected in series with the source 6 between the grid and the cathodeof the tube 20. The 5 circuit may be traced from grid 22, negativeterminal of source 6, positive terminal of source 6, conductor 34,resistance 3| to cathode 2|. The regulator winding I0 is connected inseries with the secondary winding 21 of transformer 9 in the platecircuit of the tube 20. The condenser 28 'is connected in shunt to thewinding ill to stabilize the intermittent current supplied by the tube20.

The operation of the circuit is as follows: When the motor i is startedit will accelerate until the frequency of the current developed by thegenerator approaches the frequency to which the circuit 33 is tuned. Asthe speed increases, 6 the potential of the grid i8, which is normallynegative due to the bias of the source 6, is increased by thealternating voltage drop across inductance coil 30. This superposedpotential causes space current to fiow in the detector tube producing avoltage drop in the coupling resistance 3|. This voltage is impressedupon the normally negative grid 22 of the amplifier 26, causing spacecurrent to flow in the amplifier tube and consequently in the regulatorfield I0. This cur- 7:

from this point, the, current through the regulator field I0 is variedto correct the tendency of the motor speed to change. For example, if,due

to a change in load or voltage, the speed of the motor decreasesslightly and accordingly the frequency of the current in the winding l5of the generator I l, the alternating component of the potential of thegrid l8 of the detector tube is decreased causing a correspondingdecrease in the voltage drop across the resistance 3| and a consequentdecrease in the variablecomponent of the potential of the grid 22 of theamplifier tube, thus resulting in a decrease in the current through theregulator fleld I0 which limits the tendency of the motor to furtherdecrease in speed, as would occur in normal unregulated operation.

Since the frequency of the variations impressed upon the grid of thedetector tube I6 is greater than the frequency of the variationsimpressed on the plate there will be variations of potential of bothsigns impressed upon the grid during the intervals when the plate ispositive. In order to prevent a balance of effects due to the positiveand negative potential alternations of the grid, the tube must be causedto function as a detector, that is, it must operate on the curvedportion of its characteristic.

In order to prevent distortion of the image formed upon the eye of theobserver 52 it is necessary to maintain the discs 56 and 64 quiteaocurately in phase and, for this purpose, the disc 56 is provided withan aperture 65 which is displaced from the spirally arranged apertures55 and is located on a radius midway between the first and lastapertures of the spiral, although it may also be located at otherportions of the disc. Once per revolution of the disc 56, light from thesource 53 is directed through the aperture 65 and the opening 66 in thescreen 58 and is then reflected by mirrors 6-! so as to impinge upon thephotoelectric cell 60. The resulting current impulse generated by thephotoelectric cell is transmitted to the receiving station where it isemployed to actuate the polarized stepping relay 68 when the discs 56and 64 are out of phase. For this purpose commutator discs 69, I0 and IIhaving brushes 12, I3 and 14, respectively, are mounted on the motorshaft to which the disc 64 is secured. The periphery of the commutatordiscs 69 and 1| are made completely of conducting material, while thedisc I0 is of insulating material and has the conducting segments 15 and16 which are electrically connected to the discs 69 and II,respectively.

When the d scs 56 and 64 are exactly in phase the synchronizing impulsereaches the receiving station when the disc I0 is in the position shown,that is, such that the brush 13 engages the disc between the conductingsegments 15 and I6, and the circuit including the windings of relay 68is open. -When disc leads the disc 56 (assuming a clockwise rotation ofdisc 64 is viewed by the observer 52) the incoming current impulse willflow through the conducting segment 15 and through the winding 18 ofrelay 68 thus causing the toothed wheel 88 to be moved in a clockwisedirection as viewed in the figure and the capacity of condenser 35 to beincreased. This increase in capacity causes the natural resonance of thecircuit 33 to occur at a lower frequency. The current in this circuit isconsequently increased thus increasing the current in the regulatingwinding l 0 and reducing the speed of motor 3 as explained heretofore.When the disc 64 lags the disc 56, current flows through winding 11 ofrelay 68, which causes the capacity of condenser 35 to be decreased'andconsequently the speed of motor 3 to be increased. In order to increasethe time during which the synchronizing current flows through the relaywindings, condensers l9 and 80 are shunted across these windings. Theincoming current impulses serve to charge one of the condensers whichthen discharges through the relay winding.

It is seen that the phase correcting apparatus is inoperative when thediscs 64 and 56 are sumciently out ofphase so that the synchronizingimpulse reaches the receiving station, when a portion of the disc 10outside' of the segment spanned by the conducting portions 15 and I6 isin contact with the brush 13. In this case the switch 8| may be openedand the setting of condenser 35 varied by manually operating thearmature of relay 68 until the phase relation is within the limits ofautomatic phase correction. At this time switch Bl may be closed and thediscs at the transmitting and receiving stations will consequently bebrought accurately into phase where they are maintained.

It is to be understood that the details of the specific arrangementdisclosed above may be considerably varied without departing from thespirit and scope of the invention. For instance,

instead of employing the aperture 65 of the scannir'ig disc at thetransmitting station, an electrical contact element may be used forclosing a circuit once per revolution of the disc, thereby setting upsynchronizing impulses which are transmitted to the receiving station.These impulses may be of such an amplitude that they would overload theamplifier stage immediately following the photoelectric cell and forthis reason the impulses are preferably impressed directly on the lineor on an amplifier stage just preceding the line. Instead of employing astepping relay for varying the setting of condenser 35 an arrangementmay be' used in which phase correction is realized by periodicallyincreasing or decreasing the capacity of the condenser from its normalvalue only for the duration of the synchronizing impulse. For thispurpose the movable plate of the variable condenser may be associatedwith the armature of relay 68, so that the capacity of the condenservaries directly in accordance with the position changes of the armature.

What is claimed is:

1. In a synchronizing system, speed control means comprising variableelectrical resonance means, the response of which varies sharply with aslight variation from the resonant frequency of energy supplied thereto,means for varying the natural period .of said resonance means over arange of values between fixed limits and means under the control of thesynchronizing control station for controllingsaid last mentioned meanswhen there is a departure from synchronism.

2. In a system for maintaining a plurality of elements in synchronism,speed control means comprising a resonant circuit, the response of whichvaries sharply with a slight variation from the resonant frequency ofcurrent supplied thereto, means responsive to current transmittedthrough said resonant circuit for controlling the speed of one of theelements to be maintained in synchronisrn, means for varying the naturalperiod of said resonant circuit over a range of values between fixedlimits and means under the control of the synchronizing control station,for controlling said last mentioned means when there is a departure fromsynchronism.

3. A synchronizing system comprising a dynamo electric machine at eachstation for driving the elements to be synchronized, means associatedwith said dynamo electric 'machine for generating an alternatingcurrent, means including a resonant circuit for utilizing saidalternating current to maintain said machine at a substantially constantspeed, means at one station for varying the natural period of theresonant circuit at said station over a range of values between fixedlimits, and means at another station for controlling said last mentionedmeans and thereby determining the speed at which the machine at said onestation is maintained constant.

4. A synchronizing system comprising motive means at each station fordriving elements located at these stations, means comprising electricalresonance means for maintaining said elements at substantially the samespeed, means at one of said stations for varying the natural period ofthe resonance means at that station over a range of values between fixedlimits, and means controlled by the element at another of said stationsfor controlling said last mentioned means, thereby maintaining saidelements in phase.

5. In a synchronizing system, a transmitting and a receiving station, adynamo electric ma chine having a regulating field winding at eachstation for driving the elements which are to be maintained in phase, asource of alternating cur rent the frequency of which varies inaccordance with the speed of said machine, a frequency discriminatingcircuit, means for supplying current from said source to said regulatingfield winding through said frequency discriminating circuit formaintaining said dynamo electric machines at a substantially constantspeed, and means for controlling the constants of the frequencydiscriminating circuit at one of said stations and thereby maintainingsaid elements in phase.

6. In a synchronizing system, a plurality of elements to be maintainedin synchronism and located at diiferent stations respectively, meansassociated with one of said elements for periodically setting upelectrical impulses, electrical resonance means associated with anotherof said elements for maintaining it at a substantially constant speed,and means controlled by said electrical impulses for varying theconstants of said electrical resonance means over a range of valuesbetween fixed limits, thereby maintaining said elements in synchronism.

7. In a synchronizing system, a plurality of dynamo-electric machineswhich are to be maintained in synchronism, means associated with one ofsaid machines for periodically causing a beam of light to be directedupon a light sensitive device which, in consequence, generatescorresponding electrical impulses, an electrical circuit associated withanother of said machines for maintaining it at a substantially constantspeed, and means controlled by said electrical impulses for changing theconstants of said circuit and thereby increasing or decreasing the speedof said last mentioned machine.

8. In a system for producing an image of a field containing moving orchanging objects, a.

rotating element having unevenly spaced light transmitting portions forscanning the field or a portion of the field along groups of parallellines successively, means including said rotating element for producingan impulse of synchronizing current between groups of parallel scanninglines, means comprising a second rotatable element and a driving motortherefor for producing an image of said field of view, and meansresponsive to said synchronizing impulses for controlling the energysupplied to said driving motor, thereby controlling its speed.

9. In a system for producing an image of a field containing moving orchanging objects, scan ning means comprising a disc containing aplurality of light transmitting portions arranged around the peripherythereof, the angular distance between two of said light transmittingportions being greater than that between others, means for transmittingan impulse of synchronizing current over the same channel that isemployed for transmitting image currents, a similar scanning means forproducing images of said objects, a driving motor therefor, and meansresponsive to said synchronizing current for controlling the energysupplied to said motor to control its speed.

10. In a system for producing an image of a field containing moving orchanging objects, means for scanning the field or a portion of the fieldalong groups of parallellines successively, said means comprising a disccontaining a plurality of light transmitting portions arranged aroundthe periphery thereof, the angular distance between two of saidlighttransmitting portions being greater than that between others,electro-optical means for producing an impulse of synchronizing currentbetween said groups of parallel scanning lines, image producing meanscomprising a rotatable element to be maintained in synchronism with saidscanning disc, 2. driving motor for said rotatable element, and meanscontrolled by said synchronizing current for controlling the energysupplied to said motor to control its speed.

11. In a system for producing an image of a field containing moving orchanging objects, means for scanning the field or a portion of the fieldalong groups of parallel lines successively, said means comprising a.rotating disc containing a plurality of spirally arranged lighttransmitting portions the angular distance between two of which isgreater than that between others, an auxiliary light transmittingportion aligned on a radius passing between said two widely separatedportions and means for transmitting light through said last mentionedportion to produce synchronizing impulses.

12. In a synchronizing system, speed control means comprising variableelectrical resonance means, the response of which varies sharply with aslight variation from the resonant frequency of energy supplied thereto,means for varying in steps the natural period of said resonance meansover a range of values between fixed limits, and means under the controlof the synchronizing control station for actuating said last mentionedmeans when there is a departure from synchronlsm.

13. In a system for maintaining a plurality of elements in synchronlsm,speed control means comprising a resonant circuit, the response of whichvaries sharply with a slight variation from the resonant frequency ofcurrent supplied thereto, means responsive to current transmittedaotdeee through said resonant circuit for controlling the speed of oneof the elements being maintained in synchronism, means for varying insteps the natural period of said resonant circuit over a range of valuesbetween fixed limits and means under the control of the synchronizingcontrol station for actuating said last mentioned means until thecondition of synchronism is established.

14. In a synchronizing system, a plurality of elements to be maintainedin synchronism and located at difierent stations respectively, meansassociated with one of said elements for periodically setting upelectrical impulses, electrical resonance means associated with anotherof said elements for maintaining it at a substantially constant speed,and means controlled by said electrical impulses for varying in stepsthe constants of said electrical resonance means over a range of valuesbetween fixed limits thereby maintaining said elements in synchronism.

15. In a system for producing images of a field of view, the aspects ofwhich may be changing, a rotatable scanning element having lighttransmitting apertures for'repeatedly scanning said field of view andhaving an opaque portion for interrupting the scanning betweensuccessive scannings of the field of view, means for producingsynchronizing current only during the period that said scanning isinterrupted, a second rotatable element to be maintained in synchronismwith said first rotatable scanning element, a direct current drivingmotor for said rotatable element, a speed control winding for saidmotor, and means responsive to said synchronizing current forcontrolling the amplitude of the current supplied to said speed controlwinding, thereby controlling the speed of said motor.

16. In a system for producing images of a field of view the aspects ofwhich may be changing, a source of lightand a rotatable scanning elementhaving light transmitting apertures arranged therein for directing lightfrom said source to elemental areas in succession of said field of viewand an opaque portion for preventing the illumination of said field ofview for a period between successive scannings of said field of view,light sensitive means for receiving light from the successivelyilluminated elemental areas of said field of view to produce an imagecurrent, and means directing light upon said light sensitive meansduring the period that said illumination of the field of view isinterrupted for producing synchronizing current.

17.111 a system for producing images of a field of view the aspects ofwhich may be changing, a source of light and a rotatable scanning dischaving light transmitting apertures arranged therein along a spiral pathfor directing light from said source to elemental areas in succession ofsaid field of view and an opaque portion for preventing the illuminationof said field of view for a period between successive scannings of saidfield of view, a light sensitive element for receiving light from thesuccessively illuminated elemental areas of said field of view toproduce an image current, means for pro,- duclng synchronizing currentduring the periods that the illumination of said field of view isinterrupted, a similar rotating scanning disc and a driving motortherefor at another station, and means at said other station controlledby said synchronizing current for controlling the amplitude of thecurrent supplied to said motor to maintain said scanning discs insynchronism.

18. Television apparatus for producing images of a field of view at arate such that each image is produced within the period of persistenceof vision, comprising a source of current comprising time-separatedportions of image current corresponding to the tone values of elementalareas of a field of view and portions of synchronizing current occurringbetween successive image portions, means for producing light theintensity of which is controlled by current from said source, movableimage synthesizing means for directing light from said light producingmeans, a motor for driving said image synthesizing means, and means forcontrolling the amplitude of the current supplied to said motor undercontrol of the synchronizing portions of said source of current, therebycontrolling the speed of said motor.

19. Television apparatus for producing images of the field of view at arate such that each image is produced within the period of persistenceof vision, comprising a source of current comprising time-separatedportions of image current corresponding to the tone values of elementalareas of a field of view and portions of synchronizing current occurringbetween successive image portions, means for producing light theintensity of which is controlled by current from said source, movableimage synthesizing means'for directing light corresponding to the imageportions of said current and for intercepting light corresponding to thesynchronizing portions of said current, a motor for driving said imagesynthesizing means, and means for controlling the energization of saidmotor under control of the synchronizing portions of said source ofcurrent, thereby controlling the speed of said motor.

20. A scanning disk provided with a series of scanning openings spirallyarranged therein, the ends of the series of such openings having a blanksector therebetween,the scanning disk being also provided with asynchronizing aperture disposed in a predetermined'relation to suchblank sector, but not within the series of scanning openings.

EDMUND R. MORTON.

